1. Field of the Invention
This invention generally relates to a scan module for use in an electro-optical scanner for reading indicia having parts of different light reflectivity such as bar code symbols and, more particularly, to an arrangement for, and a method of, providing shock protection and vibration isolation for the scan module.
2. Description of the Related Art
A bar code symbol scanner of the type exemplified, for example, by U.S. Pat. Nos. 4,251,798; 4,360,798; 4,369,361; 4,387,297; 4,593,186; 4,496,831; 4,409,470; 4,808,804; 4,816,661; 4,816,660; and 4,871,904, supports various electrical, mechanical and optical components in a scanner housing. These components are operative for directing a light beam from a light source onto a coded symbol for reflection therefrom. En route to the symbol, the light beam may be directed to, and reflected off, a movable scan mirror which is moved repeatedly by a drive component to cause the light beam to repeatedly scan the symbol. Light reflected off the symbol is collected by a collection optical component, and is directed to a detector component to generate an electrical symbol. Decode and microprocessor components are provided to decode the electrical symbol in accordance with an algorithm to generate data corresponding to the symbol being scanned.
In order to keep manufacturing costs down, improve reliability and facilitate the transfer of scanning technology to a variety of scanner housings of different shapes and sizes, it is known, for example, from U.S. Pat. No. 4,930,848 to assemble various electrical, mechanical and optical components on a distinct scan module, which can thereupon be positioned as a modular unit in a scanner housing. In order to protect the interior scan module from the impact of exterior shock forces externally applied to the housing, for example, if a user drops the housing or forcefully places the housing on a countertop, it is known to position relatively stiff, shock absorbers between individual components and the housing, as well as between interior support structures for the components and the housing. Although the known shock absorbers me generally satisfactory for their intended propose, as the scan modules and their components become smaller in size, lighter in weight and more energy efficient, these highly efficient, compact, lightweight scan modules, and their use of resonant and non-resonant components, become more prone to shock damage and optical misalignment.
Another related problem concerns vibration. The scan module, also known in the industry as a "scan engine," generates vibrations during scanning a symbol. Thus, the movable scan minor and its drive component create high frequency (on the order of 280 Hz) vibrations during scanning. These high frequency vibrations are not dampened by the prior art shock absorbers, but instead are propagated through the absorbers to the housing and, in the case of a hand-held housing, to the user's hand. Such vibrations are potentially irritating to the user who may find it uncomfortable to hold such a vibrating instrument, especially for prolonged periods of time.